Acrylonitrile-butadiene-styrene (ABS), methyl methacrylate-butadiene-styrene (MBS), acrylate-styrene-acrylonitrile (ASA), acrylic impact modifier (AIM), etc. that are manufactured through emulsion polymerization have superior impact tolerance, strength, fluidity, etc., and are used extensively for reforming agents of various kinds of plastic materials. Although such graft copolymers are manufactured through emulsion polymerization, it is necessary to recover polymers in the dried powder form for melting and mixing with other resins.
Usually, one of the methods of recovery of dried powder of polymers from the latex obtained through emulsion polymerization is a method of recovery through dehydration and drying by adding an aggregation agent to the above latex and aggregating the graft polymers in the latex. However, this method of recovery of the polymer powder from the latex by adding an aggregation agent has been problematic in that it has been necessary to have the aggregation process, washing or dehydration process of the aggregation agent, and drying process until the polymers have been recovered in the dried powder form since polymer particles have been coagulated in water usually; facility expenses have been high; and it has not been easy to manage operation of the above processes.
Also, an excessive amount of waste water has been generated during the aggregation process as well as washing and dehydration processes, and it has required for an excessive amount of energy since the aggregation process has been performed at a high temperature. Further, there have been problems such as formation of chromophoric groups, generation of matrix adhesive materials, lowering of luster, etc. since the aggregation agent has remained in the polymer powder recovered from the latex by administering an aggregation agent such as inorganic salts such as aluminum chloride, sodium sulfate, sodium nitrate, calcium chloride, etc. or sulfuric acid, etc.
Another method of recovery of polymers in the dried powder form from the polymer latex is a process of spraying and drying the polymer latex directly with hot air. This process enables obtaining of dried powder from a polymer latex manufactured through emulsion polymerization at a time. It is a preferred process industrially in view of the simplicity of the process, installation expenses, and management of its operation.
The method of recovery of powder from the polymer latex through spraying and drying is disclosed in European Patent No. 1,201,692. Disclosed in this patent is a method of manufacture of a powdered composition of a high rubber impact controlling agent in which the weight fraction of the rubber phase is 90 weight % or greater through spraying and drying of a latex containing two kinds of core-shell polymer particles of which average particle diameter differs by 50% or greater. It has been reported that the high rubber impact controlling agent powder manufactured through spraying and drying as described in the above has been advantageous in that it has required for a less amount of a flowing builder in offering compaction-free powder.
Also, disclosed in Japanese Patent No. 2002-363292 is a method of recovery of polymer powder through spraying and drying of a polymer latex by controlling the temperature of the outlet portion of a spraying drier, separating and recovering polymer powder, aggregating moisture by supplying a part of exhaust gas to the aggregation device, heating and re-circulating, and controlling the concentration of oxygen in the spraying drier to be 5 volume % or less.
Further, disclosed in Japanese Patent No. 2002-226595 is a method of manufacture of diene graft polymer powder through spraying and drying of a diene graft polymer latex economically without worrying about ignition of the diene graft polymer by automatic oxidation, etc. in the drier by spraying the diene graft polymer latex into the drier and sending overheated water vapor to the inlet portion of the drier at the same time.
Still further, disclosed in Japanese Patent No. 2001-213969 is a method of reducing the amount of generation of fisheye while improving re-dispersibility during melting and mixing in the method of recovery of powder by spraying and drying of an emulsion polymerization latex of which main component is an acrylic polymer by lowering aggregation of the surface of acrylic resin composition powder by using overheated water vapor for heating gas for drying.
The conventional process of recovery of polymer powder by administering an aggregation agent is composed of the processes of aggregation, washing and dehydration, and drying. And therefore, it is possible to obtain powder from which most of impurities such as surfactants, electrolytes, etc. is removed. However, inasmuch as spraying and drying is a process of manufacture of dried powder of polymers by removing aqueous dispersion materials from the polymer latex manufactured through emulsion polymerization by using a heated gas, the powder manufactured through spraying and drying naturally contains an excessive amount of impurities such as surfactants, electrolytes, etc. added in view of characteristics of emulsion polymerization.
Accordingly, the dried powder manufactured through spraying and drying has had a problem of inferior thermal stability due to surfactants, electrolytes, etc. remaining in the dried powder. Particularly, it has been problematic that the surfactant remaining in the polymer powder has lowered the thermal stability during melting and mixing it with other resins.
When melting and mixing the polymer latex polymerized by using a non-reactive surfactant with other resins by using the polymer dried powder manufactured through spraying and drying, there occurs a phenomenon of lowering of the quality of appearance such as shining of the final product, etc. as the movement of the surfactant remaining in the dried powder becomes free. Also, the surfactant that can move freely as it remains in the dried powder has had a problem of lowering of strength of the final product as it has assumed the role of a plasticizer.
The above-described patent still had a problem of failing to present a method of solution for lowering of thermal stability due to the surfactant remaining in the polymer dried powder manufactured through spraying and drying.
In the meantime, the inventors of the present invention have found that it has been possible for a small amount of a surfactant to secure the stability of the latex through chemical bonding, not physical absorption, if it has been a reactive surfactant, and it has been possible to prevent lowering of thermal stability due to a surfactant during melting and mixing of the dried powder manufactured by using a reactive surfactant with other resins.